Shape of Tree Trunks and Branches

B. C.

Shape of Tree Trunks and Branches

BY DELBERT W. PARRATT, B. S.

Look at these drawings. Notice that "A" tapers as it goes from the ground upwards, "B" is practically cylindrical, and "C" flares as it goes from the ground upward. Which most nearly represents the shape of the ordinary trunk of our common trees? This is what Thad Wisemar's teacher asked her pupils yesterday. Every one answered "A." The question was then carried to other and higher rooms of the school where more than two hundred and fifty pupils likewise answered "A" and only four spoke in favor of "B." Nobody gave "C." When the returns of the "vote" were announced, Thad and all his room companions expressed a sense of satisfaction on find- ing that none of the four "votes" for "B" were from their room. — Only the teacher seemed quite indifferent no signs of approval or disapproval were noticeable in her manner. She calmly sug- gested that sometimes the minority is in the right, and urged her enthusiastic hearers not to vent their applause until first mak- ing sure of their ground. "We are sure now," responded Thad after gaining due recog- nition from the lady in charge, "all the tree trunks around our place are just like 'A.'" "Very well," tactfully injected the teacher," perhaps there are some here who have never looked at a tree trunk with this thought in mind, so let us leave this question till tomorrow. In the mean- time will all make it a point to observe tree trunks ?" Thad was so thoroughly satisfied that his answer was correct that he did not even take pains to verify his conclusion by so much as consciously glancing at one of the many tree trunks on the way home from school. He "knew" and therefore why should he look? As a matter of fact, after leaving school he gave no

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thought to the question until upon reaching home when he was greeted with, "Well, Thad, this is your nature study day. Did you have any more questions about trees ?" "Yes," answered Thad, "the other pupils are to find the answer. I already know." "What is the question?" queried Vaughn Wisemar, Thad's older brother. "Here it is," came the reply as Thad pulled out his pencil and drew three sketches similar to those made by his teacher. "Which of these is most like an ordinary tree trunk?" "Which did you say?" retorted Mr. Wisemar. "Why, 'A' of course !" replied Thad with utmost confidence. "Anybody who has ever seen a tree knows that!" "You are sure then that you have seen a tree. Thad, I believe you are right but you know we were 'caught' by two other simple questions on trees. You remember the one about life in a big tree trunk, don't you ? And also the one about sap in the winter time ? We were 'sure' of our answer then, and yet we were both wrong, weren't we? Let's look at some tree trunks this time before being 'sure'." "That's easy to do," came from Thad as both turned toward the open door. Both centered attention upon the firsttree encountered —the box elder near the kitchen window. Both looked surprised. The trunk was like "B" and not like "A." The old apple tree's trunk was like "B" and so were those of the poplar and pear trees. Tree after tree was examined and in every instance the trunk, while more or less crooked, was about cylindrical and not appreciably tapering. At length, however, Thad found one giving evidence of tapering but upon closer examination it was found that the apparent tapermg was due to the removal of some branches. So Cross sections B and C after making careful study of a great equal approximatelycross many trees in the neighborhood, both section Across sections E ; Thad and Mr. Wisemar concluded that and Dequal approximately- cross section B cross sections ; tree trunks are of about the same F and G equal approximately thickness throughout their lengths and cross section D, etc. that there is no pronounced tapering, suggestive of inverted, parsnips, as is commonly believed. They also noticed that many trunks enlarge — flare out — just before

450 IMPROVEMENT ERA entering the ground which, of course, is clue to the branching of the trunk into roots just as the trunks often enlarge at the top when dividing into scaffold limbs. While making this little study, our two amateur naturalists discovered that each of the scaffold limbs was also a crooked cylinder like the trunk. The same was true of the main limbs and also all the branches and even the twigs. This being the case, Mr. Wisemar concluded his preconceived notion that a tree gradu- ally tapers from the ground up, through the trunk, and out through the various branches was erroneous and that in reality the decreasing in size, step by step, from section to section. The reduction in every instance came only where the limb gave off a branch or where the branches were divided and subdivided and then, in every case, reduction was equal to the amount contained in the branching bough or twig. Alittle rough measuring and figuring demonstrated the fact that the amount of cross section material in all the scaffold limbs put together was not far from equaling that of the trunk. The same was true of the cross section material of the main branches compared with that of the support- ing scaffold limb. And, moreover, this relationship carried right out through the smaller branches and even to the terminal twigs. "Then," reasoned Mr. Wisemar, "the sum of all the cross section areas of all the main branches, or of the minor branches, or even the twigs of a perfect tree— a tree from which no parts have been — removed must be approximately the same as the cross section area of the tree's trunk." These new discoveries he explained to Thad, and while doing so marveled at what little they both had ordinarily seen of the beautiful, companionable trees so common in their experiences. He wondered if most people, like himself, "have eyes and see not." This morning Thad anxiously hurried off to school. He had some new ideas and, like all normal children, could hardly wait to impart these ideas to his fellow school associates. He willingly withdrew his former statement relative to tree trunk shapes and gladly explained what he and his big brother had learned regard- ing the sreneral structure of trees.